You won't see any cages with dogs (or any cages) in them FOR SURE. And no, the old men probably won't talk to you because you don't speak Korean. Not to mention they're probably drunk and surly. If anyone has a foreigner prejudice, it's usually them haha.

You will only see a tiny restaurant with the letters 보신탕 on the outside. That's it. No dog pictures, no nothing. A lot of places that sell it also sell other soup more prominently and those letters might be tiny or barely visible.